linux-kernel - Re: [PATCH] MMC: Flush mmc workqueue late in the boot sequence

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Message-ID: <46432212.9070008@drzeus.cx>
Date:	Thu, 10 May 2007 15:45:54 +0200
From:	Pierre Ossman <drzeus@...eus.cx>
To:	Haavard Skinnemoen <hskinnemoen@...el.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MMC: Flush mmc workqueue late in the boot sequence

Haavard Skinnemoen wrote:
> 
> What exactly makes this unreliable? This is done almost exactly the
> same way for SCSI. See drivers/scsi/scsi_wait_scan.c.
> 

I am not against the function of waiting for an initial scan, what I oppose is
using side effects to achieve that function. I do not want to take
responsibility for something that easily breaks because we use a kernel
subsystem for something it wasn't meant for.

That said, if there is a precedent for achieving this function a certain way, I
might be convinced to let it in. I'll have a look at that scsi example.

> 
> I don't know about USB, but root=/dev/mmcblk0p1 used to work before
> 2.6.20 and it doesn't work anymore. Doesn't that make this a regression?
> 

Yes and no. It depends on if it was an official function, or just an effect of
how things currently were implemented. As far as I can see, it's the latter. The
MMC layer goes through several steps that could very well get delayed or happen
in parallel. So the fact that it happened to work the way you wanted it to was
sheer luck.

Rgds
Pierre

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